extract one single file and its history from a repo

[Uwe Brauer]

   > On Thu, Sep 29, 2016 at 8:30 PM, Uwe Brauer <oub at mat.ucm.es> wrote:

   > It looks like export only exports whole changesets. You probably want
   > to use "hg convert" with a filemap that just specifies your single
   > file.

   > https://www.mercurial-scm.org/wiki/ConvertExtension#A--filemap

Thanks cool. I still think that it would be convenient if export had
such an option, but since I cannot provide a patch, I better shut up.